Re: [Valgrind-users] Make Lackey Faster

[Peng Du <imd...@gm...>]

Nick

Thanks for the hints. The penalty is expected. I've played with PIN and
its pinatrace and MemTrace tools for a while. They worked and the
performance is not too bad, though a bit slower than Valgrind. 

I need the virtual address of the read/write. Hence, HW counters can't
do the job. I did considered the Precise Event Based Sampling (PEBS).
But only L1/2 cache load miss events are supported by PEBS. So it can't 
do the job either. 

If HW counters could work, it would the best solution since it is
most light-weight. Now my 2nd choice is binary instrumentation frameworks
like Valgrind. 

Now I still have a questions: is the memory trace generated by Valgrind
or PIN representative enough to model real program behaviours, considering 
multi-threading? 

Thanks 








On Tue, 18 Aug 2009 08:24:47 +1000
Nicholas Nethercote <n.n...@gm...> wrote:

> On Tue, Aug 18, 2009 at 7:18 AM, Peng Du<imd...@gm...> wrote:
> > Hello, everyone
> >
> > A newbie question, according to Valgrind's manual for the lackey
> > tool:
> >
> > "It (lackey) could be made to run a lot faster by doing a slightly
> > more sophisticated job of the instrumentation ..."
> >
> > Now I need a very simple memory read/write counting tool, just like
> > lackey. But the tool has to be fast.
> >
> > Can anyone elaborate a little on how to make lackey A LOT FASTER? Or
> > has anyone done so? If yes, do you mind sharing the source?
> 
> I see two possibilities:
> 
> - Currently there is one C function call per original instruction.
> You could batch these up to a degree, eg. count multiple instructions
> with a single C function call.  Cachegrind does something like this.
> 
> - You could use inline (Vex IR) instrumentation rather than C function
> calls.  See VEX/pub/libvex_ir.h for details of Vex IR.
> 
> You could also do both of these together.  Doing so is left as an
> exercise to the reader.
> 
> Even if you do all that, the tool would still have a significant
> slowdown -- the limit case is Nulgrind (--tool=none) which does no
> instrumentation and typically has a 5x slow-down.  I don't know if
> that is fast enough for your purposes.  You could look at Pin or
> DynamoRIO as alternative instrumentation frameworks that are better
> suited to simple tools such as the one you need.  Pin in particular
> may have such a tool included in its distribution.  Or you could look
> at hardware program counters, if they provide the information you
> need.
> 
> Nick